Electrical apparatus



Feb. 8 `1927.

Patented Feb. 8, 1927.

UNITED STATESV Pfrlur Fries. f

CHARLES G. SMITH, 0F MEDFORD, MASSACHUSETTS, ASSIGNOR, BY MESNE ASSIGN-MENTS, TO RAYTHEON MANUFACTURING COMPANY, 0F CAMBRIDGE, MASSACHU- SETTS,A CORPORATION 0F MASSACHUSETTS. y

ELECTRICAL ArPARATUs'.

Application mea April 25, 1921. seriai Nn. 464,359.

The present invention relates to electrical apparatus and moreparticularly to apparatus of the type disclosed inthe copendingapplications of Smith, Serial No.' 415.536, filed October 8, 1920. andSerial No. 418,263, filed October 20, 1920.

As disclosed in the applications above rcferred to, it is possible todesign and locate electrodes immersed in a gas in such a manner thatgaseous conduction due to ionization of the gas may not take place evenat high potential differences. This normal insulating state, however,may be changed to a conducting state by introducing a magnetic field inthe space separating the electrodes., If the electrodes are in the formof cylinders immersed in a gas with a radial electric field between thecylinders and a magnetic field substantially parallel to the axes of thecylinders, then for a certain range of magnetic iield strength the tubewill freely conduct with the outer cylinder at a negative potential butwill insulate against high potential differences when the4 innercylinder is at a negative potential. It will be obvious to those skilledin the art that this form of tube is thus adapted for the rectificationof alternating currents.

It has been discovered that the employment of a non-uniform or spacevarying magnetic field in a tube of this character having cylindricalelectrodes positioned with their axes coincident markedly increasestherectiying properties of the tube and permits rectification to take placeover a considerable range of magnetic field .strength and a great range'of gas pressures within the tube. Such a tube may be caused to rectiiyalternating currents with either the inner or outer electrodes negativeproviding that the magnetic field is non-uniform and strongest adjacentthe negative electrode. In the preferred embodiment of the invention thetube is provided with concentric cylindrical electrodes and a spacevarying magnetic field with its strongest portion adjacent the outerelectrode and its weakest portion -adjacent the inner electrode. Thistype of tube will rectify with permissible variations of magnetic fieldstrength and gas pressure approximating ten to one.

In its broadest conception the invention contemplates the employment ofa non-uni'.-

lows: In an apparatus of this character the separation of the activesurfaces of the electrodes approximates the order of magnitude of themean free path of the electrons, this `path varying in accordance withthe character of the gas employed and the pressure to which .this gas issubjected. The employment of a magnetic field which is strongest at theouter cylindrical electrode and weakest at the inner electrodesubstantially lengthens the path of electrons leaving the outerelectrode whenthe latter acts as a cathode and shortens and constrictsthe path of electrons leaving the inner electrode when' this latterelectrode is acting as a cathode. In this manner the paths of electronsleaving the outer cylinder are sufficiently lengthened to insurecumulative ionization and consequent gaseous conduction and, on thelother hand, the paths of electrons leaving the cathode when the innercylinder is negative are not sufiiciently long to produce cumulativeionization and gaseous conduction in the oppositeA direction.

In the accompanying drawings illustrating the preferred form of theinvention Fig. 1 represents a sectional elevation of a tube embodyingthe features of the invention; Fig. 2 is a simple circuit embodying thetube; and Figs. 3 and 4 are partially diagrammatic views illustratingthe approximate path which it is believed the electrons follow when thetube is employed as a rectifier.

. Referring to the illustrated embodiment of the invention it will beobserved that the bulb or tube 10 contains steel cylinders 12 and 13separated by a small air gap and connected together by a sleevek 14 ofco per or other non-magnetic material having eat radiation openings 16formed therein. The outer electrode comprises a short tube of molybdenumor other suitable electrode material gripped within the cylinders 12 and13, as indicated, opposite the openings 16.

The inner electrode comprises a copper tube 20 which may be spun onto apiece 22 of silica glass which is in turn held in proper relation to thesteel cylinder 12 by a copper spacing member 24 spun thereon andprovided with annular flanges 26. The steel cylinders are retainedwithin the opposlte reduced ends of the bulb 10 by flexible holdingrings 28 and 29. lThe inner and outer electrodes are respectivelyconnected with leads 32 and 33 passing out of opposite ends of the tube,the lead 32 being connected to one end of the cylinder 12 and the lead33 being connected within the enlarged mouth formed in the lower end ofthe inner electrode 20. The tube may be connected into appropriate formof circuitv where it may be desired for example to rectify analternating current of five hundred volts or more.

The magnetic field' parallel to the axes 'of the electrodes may beconveniently introduced by a permanent magnet 35 positionedapproximately as shown and operating in conjunction with the cylinders12 and 13 of magnetic material to 'introduce a non-uniform magneticfield in the space separating the electrodes 18 and 20, this field beingweakest adjacent the surface of the inner electrode 20 and becomingprogressively stronger as the outer electrode is approached. Uponreferrig to Fig. 2 a simple form of circuit embodying the tube as arectifier is shown, this circuit conveniently comprising an inputcircuit indicated at 40 capable cf delivering alternating current to theprimary of a step-up transformer 42, the secondary of which is embodiedin an output circuit containing the tube whicl rectifies the highvoltage alternating current delivered thereto. This output circuit maybe connected with any desired form of load circuit (not shown) toutilize the high voltage current so rectified.

Upon referring to Figs. 3 and 4 it will be observed that the electronsleaving the outer or negative terminal start in a region of strongmagnetic field and their path is accordingly bent or curved quiterapidly. As they continue to move toward the inner electrode or anode,however, they pass into a region of less magnetic field and their pathbecomes straighter until it is substantially parallel to the plane ofthe anode, alter which the electron moves over a comparatively long flattopped path adjacent the anode, which form of path is ideal forproducing positive ions near the anode which drop to the cathode. On theother hand, with the same character of magnetic field and with the innerelectrode negative, electrons leavino the cathode start off in astraight pat ltoward the anode or ,outer electrode and then pass into aregion of progressively stronger field where the electron is shortlybent back in a sharp curve and caused to return to the inner electrodeor cathode from whence it started. Owing to the comparatively shortdistance which these electrons travel with respect to the length oftravel of the electrons leaving the outer electrode it is a relativelysimple matter to cause rectification over a wide range of pressureswhere the magnetic field is varying in space and strongest adjacent theouter electrode. As a matter of act-ual fac-t it has been observed thattubes of this character rectify successfully with gas pres sures rangingfrom three-tenths of a millimeter to two-thousandths of a millimeter.

It should be understood by those skilled in the art that thecharacteristic properties of a magnetic field having its strongestportion adjacent onefelectrode and becoming progressively weaker as theopposite electrode is approached are capable of embodiment in a widerange of constructions employing cooperating electrodes immersed in agas, this type of magnetic field causing a tube to conduct when theelectrode in the region of strongest magnetic field acts as' a cathodeand to insulate when the electrode in the region of weakest magneticfield is acting` as a cathode. Y

In a generic sense, the term hollow cathode includes a cathode whoseactive surface only partially surrounds a gaseous medium so that themedium immediately adjacent the active surface is more or less pocketedor confined.

A feature of the invention consists in that the field is stronger nearthe inner concave surface of cathode 13 than adjacent the outer convexsurface of the anode 20.

I claim- 1. Gaseous conduction apparatus comprising a hollow cathode, ananode presented to the interior of the hollow cathode, means forcreating an electric field between the surfaces of the electrodes, andmeans for introducing a non-uniform magnetic field in the spaceseparating the electrodes which is strongest adjacent the cathode andbecomes progressively weaker as the anode is approached.

2. Gaseous conduction apparatus comprising an electrode having a curvedsurface, a second electrode having a similarly curved surface on theconvex side of the first electrode, means for creating an electric fieldin the space separating the curvedsurfaces of the electrodes, and meansfor introducing a magnetic field in the space separating the electrodeswhich is stronger near the inner surface of the concave electrode thanadjacent the outer surface of the convex electrode.

3. An electrical apparatus comprising a gas filled tube, inner and outercylindrical electrodes received within the tube and located with theiraxes substantially coincillU dent, means for creating an electric fieldin the space separating the electrodes, means for introduclng a magneticfield into the annular space separating the electrodes, and cylinders ofmagnetic material positioned concentric with the electrodes and arrangedadjacent one of the electrodes to cause the magnetic field to benon-uniform between the electrodes. v

4. An electrical apparatus comprising a gas filled tube, .an innerelectrode member, an outer electrode .cylinder supported concentricallywith the inner electrode member, cylinders of magnetic material arrangedoutside of the outer electrode, and means for lcreating a magnetic fieldwhich is intro-` duced into the annular space between the electrodes bythe cylinders of magnetic material, the field being strongest adjacentthe outer electrode andV becoming progressively weaker toward the otherelectrode.

5'. An electrical apparatus comprising electrodes immersed in a gas andhaving opposing surffaces spaced apart a distance which is short andcomparable to the mean free path of electrons in the gas, and means forintroducing a non-uniform magnetic field between the electrodes.

6. An electrical apparatus comprising a gas filled receptacle, means forcreating an electric field in a portion of the gaseous region which islimited in the direction of the electric field to a length comparable tothe mean free path of electrons in the gas,

impressing a magnetic field between the electrodes, and magneticmaterial placed adjacent one of the electrodes so that the magneticfield is strongest adjacent that-felectrode and becomes progressivelyweaker toward the other electrode.

8. Electrical apparatus comprising spaced electrodes with gastherebetween, the disvtance between the electrodes being of the order ofthe mean free path of electrons in the gas, and means for producing, insaid space, a magnetic field which varies in intensity from oneelectrode toward the other electrode.

9. Electrical apparatus comprising inner and outer electrodes with anannulaidischarge space therebetween, containing gas, the distancebetween the electrodes being of the order of the mean free path ofelectrons in the gas, and means for producing a magnetic field whichextendsl predominantly in the direction of the axis of said annular'space and which varies in intensity radially of the annular space. l

CHARLES G. SMITH.

